1. Field of the Invention
This invention relates generally to keyboard assemblies, and more particularly to a flush lighted flat keyboard assembly.
2. Description of the Prior Art
Keyboard assemblies of the type employed in electronic calculators and for digital control of appliances such as microwave ovens and television receivers, commonly comprise an array of momentary-contact switches mounted on a printed circuit board. Conventional keyboards employ individual push buttons at each key station which are contained by an escutcheon plate, each keytop protruding through an opening in the escutcheon to allow sufficient travel for switch actuation when pressure is applied. U.S. Pat. No. RE 29,440, assigned to the assignee of the present invention, discloses such a keyboard assembly.
In order to insure operation of the conventional keyboard over a wide temperature range, adequate clearance must exist between the keytops and the escutcheon in order to compensate for dissimilar coefficients of thermal expansion and contraction; however, with such clearance, the device becomes susceptible to contamination by moisture, sand, dust, etc. which may prevent reliable switch actuation. Conventional keyboards are also vulnerable to vibration and shock; normal reliable operation requires nearly a free-floating keytop which may become abraded by the escutcheon in response to shock or vibration, the process being accelerated at the resonant frequency of the key mass. Shock or vibration can also cause damage or destruction to sensitive switching elements beneath the key. Form-fitting boots have been tried to protect the keytops from moisture, sand, dust, etc.; however, such boots must be flexible to allow acceptable operational perforance and thus, offer little improvement with respect to shock and vibration.
In order to eliminate the problems above-described, flat keyboard assemblies have been proposed in which the push buttons are replaced by a relatively thin, flexible member having one side in facing relationship with the switch elements so that deflection of the member in a particular area in response to force manually exerted on the other side of the member actuates a respective switch element. U.S. Pat. No. 4,071,718 to the present inventor and also assigned to the assignee of the present application, discloses a flat keyboard assembly incorporating a flexible switch-actuated member between the flat keyboard member and the switch elements, the switch-actuating member having switch-actuating projections thereon respectively in alignment with the switch elements and isolating projections intermediate the switch-actuating projections which inhibit false actuation of another switch element when force is exerted on the keyboard member at a particular location associated with a particular switch element.
There are applications for flat keyboard assemblies in which it is desirable to provide lighting at all or selected ones of the key stations. For example, it may be desirable to illuminate all of the key stations for night operation or, it may be desirable to illuminate a particular key station in response to actuation thereof. Further, in certain computer-associated applications, it is desirable to provide a programmable keyboard assembly wherein the indicia for a particular key station may be changed in accordance with a computer program. Such an application requires selective alpha-numeric illumination of particular key stations.